1. Field of the Invention
This invention relates to systems for generating electrical power and, more particularly, to systems for locally generating electrical power to augment incoming power having sustained periods of low level.
2. Description of the Prior Art
A substantial portion of modern-day technology depends for its operating power on commercially supplied ac power sources. Sometimes, however, a commercial ac power source fails catastrophically, resulting in blackouts, or fails only partially, resulting in brownouts or transients. A blackout is a condition of absolute power failure. A brownout is a condition of significantly reduced output voltage. A transient is a momentary surge or dip in the power level due to substantial but short disturbances at the generating equipment or on the power line.
Power level variations as described above can significantly affect equipment and may, in some instances, damage the equipment. In communication circuitry, even a transient interruption or surge may cause undetected errors in data or control signals or cause damage that is not readily detectable or obvious. To protect against those hazards, uninterruptable power supplies (UPS) are often employed. A UPS guarantees the continuity of power regardless of the performance of the primary commercial ac power source upon which the customer generally relies.
A commonly used UPS is the continuous type power supply in which a rectifier charger, powered by a primary commercial ac power source, continuously energizes an inverter circuit. The inverter circuit operates to supply output power. A battery is connected across the output of the rectifier charger to supply the necessary dc power to the inverter, should the primary commercial ac power source vary significantly or fail.
Another type of UPS operates in a parallel continuous arrangement in which two independent sources, a primary commercial ac power source and a secondary reserve ac power source, operate continuously in parallel. These two ac signals are combined and supplied to the load continuously. Should one fail, the remaining operative source takes over to supply the partial or the full load, as necessary. An example of this type of UPS is disclosed by R. E. Kuba in U.S. Pat. No. 3,398,292, issued Aug. 20, 1968.
Still another type of UPS is the transfer type. In the transfer type UPS the full power to the load is normally supplied by the commercial ac source. When the commercial power source is operating normally, the reserve power supply does not supply any power to the load but operates in a standby mode. When the ac commercial power fails, the auxiliary power, which generally comprises a dc source connected to an inverter, is connected to supply the power to the load and the commercial ac power source is disconnected from the load. Transfer type UPS systems are disclosed, for example, by R. Schumacher et al. in U.S. Pat. No. 3,229,111, issued Jan. 11, 1966, and by R. S. Jamieson in U.S. Pat. No. 3,348,060, issued Oct. 17, 1967.
The above solutions to degradations in power levels supplied by commercial ac sources are quite effective as long as the degradations are not of sustained duration. They are not effective for sustained blackouts or brownouts because the auxiliary power in all of the above arrangements is a battery that is being discharged in the process of replacing or supplementing the commercial power. Blackouts and brownouts, on the other hand, are generally sustained failures. Blackouts generally occur when a system fault occurs which needs to be repaired, and brownouts generally occur when the generating equipment is already operating at a peak of capacity when additional power is demanded by the users, or when the power company, for whatever reasons, needs to conserve existing fuel supplies.
To ameliorate the effects of a sustained brownout, customers can increase the voltage supplied to them locally by employing a step-up transformer. This, however, is not a viable solution, for it attempts to extract additional power from an already exhausted power source. It remains, then, that in situations of sustained brownouts, required power which cannot be supplied by the commercial power source must be obtained from a plentiful and stable auxiliary power source supplied by each customer.
In view of the foregoing, it is an object of this invention to provide a stable and plentiful auxiliary power source which would reliably and effectively augment the power supplied by commercial ac power sources in cases of sustained failures.